Users have grown accustomed to using a web browser as their single and favorite interaction media for the world-wide-web. In many internet applications verification that a real human is interacting with the application is performed. A very common way to achieve this is by using a CAPTCHA test. The most common type of CAPTCHA was first disclosed in 1997 by Mark D. Lillibridge, Martin Abadi, Krishna Bharat, and Andrei Z. Broder. This form of CAPTCHA includes the user typing the letters of a distorted image, sometimes with the addition of an obscured sequence of letters or digits that appears on the screen.